1. Field of the Invention
This invention relates to a foam forming unit for use in combination with a liquid container, including a pump for air and a pump for liquid.
2. Brief Description of the Prior Art
Such a foam forming unit is, for example, known from international patent application WO 99/54054, which describes a foam spraying device for a liquid container, having an air suctioning part, a mixture chamber and a spray head with a foam outlet. A first piston-cylinder unit for air and a second piston-cylinder unit for liquid are provided between the spray head and the liquid container. Each unit is fitted with an inlet and an outlet valve. These units are coupled in such a way that they cooperate with each other.
In international patent application WO-A 97/13585 a foam dispensing device is described, which comprises a liquid container and operating unit of a concentric air pump and a liquid pump. Each pump has a piston chamber with a piston which is displaceable therein and an inlet and discharge. The operating component operates both pumps simultaneously. The air pump has a double-acting shut-off device which can be operated actively by the operating component and shuts off both the inlet and the discharge of air. It is mentioned in this document that normal valves, as passive shut-off devices which open by pressure differences generated in the unit, are not wanted and a shut-off device which can be operated actively by the operating component is a main characteristic of this foam forming unit. Moreover, although this foam forming unit can generate a good foam, i.e. a foam of correct texture, this known foam forming unit consists of a large number of construction components manufactured from different materials. The cost of manufacturing such a foam forming unit is therefore relatively high.
Further, in U.S. Pat. No. 4,057,176 a reciprocating type of finger pump for use on a liquid product container is described, which combines a tubular housing including a spray nozzle, mounted coaxially in the sleeve of an accumulator cap including a central valve. The valve opening leads to a dip tube which passes into the container. If the tubular housing is depressed, a hollow piston is driven against the tension of a spring. In order to provide an atomized spray two subsequent downward strokes are needed. This pump is only constructed to spray a liquid, although also other products like gases, vapors or powders can be atomized. However, it cannot provide a foam as in the present invention.
The object of the present invention is to improve the foam forming unit known from the prior art.